This invention relates to electrical heating apparatus and, more particularly, to apparatus for applying radiant heat uniformly to any one of a variety of differently contoured workpieces, such as the circumferences of large pipes for the purpose of relieving weld stresses in the pipe weld.
The uniform intense heating of a preselected portion of a large workpiece by known techniques presents several difficulties in that the apparatus may be massive and non-portable, the apparatus may be contoured to heat only a single shape and size of workpiece, the available temperatures may be limited to about 1500.degree. F. hot spots and other non-uniform heating effects may occur, and the entire assembly may become heated. All of these difficulties may be visualized readily by contemplating, for example, the thermal stress relieving at 1300.degree. F. of a welded joint between the abutting ends of two large pipes having, say, 6 foot diameters and wall thicknesses of 5 inches. Since rate of temperature rise and uniformity of temperature at all circumferential points must be closely controlled it is apparent that the size and mass of such a workpiece presents significant heat control problems.
In U.S. Pat. No. 3,731,051 to R. P. Ellersick, the subject matter of which is incorporated herein by reference, there is described a heating apparatus and method which overcomes the above disadvantages to a large degree as a result of the use of special modular heat generating units linked together in end-to-end relationship to form a chain-like assembly. The assembly is made up of an appropriate number of modules at the work site and then conformed to the contour of the workpiece, as by being wrapped about the circumference of a pipe to be heated. Each module comprises a radiant heating means, preferably in the form of a group of quartz iodide lamps, projecting from an air cooled housing in which the bases of the bulbs are supported and a reflector to direct heat from the bulbs toward the pipe. The quartz iodide lamps are capable of emitting high intensity radiant heat in a range of wavelengths near infra-red but sufficiently outside the latter that the escaping light rays are not harmful to the eyes. It has been found that this type of radiant heat can be rather easily controlled to give substantially more rapid heat penetration into the workpiece and greater uniformity of temperature within the workpiece than can be obtained with, for example, a resistance heater disposed in the same relative position.
In one embodiment that is disclosed the housings containing the quartz iodide lamps are joined together in end-to-end relationship to form the chainlike assembly and in another embodiment the reflections are jointed together in end-to-end relationship to form the chain like assembly. The housing portion of the module is the same in both embodiments.
Although the modules constructed as described in the above cited patent have performed in a generally satisfactory manner it has proven to be somewhat involved in disassemblying the housing portions if a lamp or a lamp socket needs to be replaced. Also, it has been found that since lamp sockets are partly exposed they are susceptible to being broken if accidently hit. Furthermore, improvement is needed in the internal electrical wiring arrangement. In addition, no means are provided for quickly disconnecting the module from its power source. Finally, when the modules are connected end-to-end by their reflectors, no means are provided for rigidly securing the housings to the reflectors.
It is the general purpose of this invention to provide a heater module of the type described in the above cited patent which overcomes the above noted shortcomings.